(1)设该直线为y=kx+k+1(k≠0)
x^2+(kx+k+1)^2/4=1
Δ=-32k+48=0
k=3/2
y=1.5x+2.5
(2)设该直线为y=1
x^2+1/4=1
Δ>0不满足条件,舍去
(3)设该直线为x=-1
1+y^2/4=1,y=0
满足条件
所以综上所述,该直线为
y=1.5x+2.5
x=-1